I've been testing Trinity the last few days, and I think it's really being slept on. Yes, it's 100 spirit, kind of confusing when you first read it, and it was straight up crashing the game at launch so I get why it got pushed aside. But it can be 50-70% more elemental damage, or 2-3 extra support gems worth of damage on all your elemental attacks.

Wall of text incoming, but I think there's some nuances to this that are important to describe beyond just damage numbers.

What is Trinity?

https://poe2db.tw/us/Trinity
Basically, Trinity has 2 buff levels for each of the 3 elements (excluding chaos), for a total of 6 possible buff levels. Each current buff level grants you up to 12% more elemental damage from just the gem and quality.
Because it removes 2 resonance from the elements that weren't the highest hit, you can only practically have 5 buff levels at any time. If you're just using one element, you'll only generate resonance for that element and cap out at 2 buff levels, or 24% more damage. Still pretty good but not as good as trying for 2 or 3 elements.

There's a lot of options for generating more resonance types, like heralds converted to types other than your main skill.

How can we use this?

The most straightforward way to generate a lot of resonance is to use Painter's Servant
https://poe2db.tw/us/Painters_Servant
My understanding of how these work is they take all of your elemental damage, add it up into one big pool then spread it evenly across fire, cold and lightning. This happens after conversions on your skill gems, so for example Lightning Spear converts 80 or 100% of physical damage to lightning, and all of that is added to the pool and split 3 ways as well. Any added flat damage is converted as well. The only thing that's outside of the even split is "damage as extra" mods, those happen after conversion.

So if you're trying to evenly split, a pair of painter's with the same roll on all elements is ideal, a single skill can raise all 3 resonance at once. Just make sure to be careful about sources of "gained as extra" like Ice Bite, Innervate, and other gear, gems or passives that can provide that, unless you want certain skills to be skewed to one element or another.

Dealing all 3 elements at once has the upside of access to all elemental ailments as well, so for example Amazon's infuse weapon, even when lightning infused is still able to freeze or ignite. Especially important in combination with Combat Frenzy, we can easily Freeze to generate frenzy charges this way.

Splitting elements does present some challenges though. Resistance shred is harder for one, there's a pretty limited amount of elemental penetration that applies to all elements, and we don't have anything like "Elemental Weakness" curse in PoE2 yet. With the penetration on the tree, and a soul core in the weapon we can hit 42% penetration which is good for most cases. Pinnacles have 50% res, and penetration can't cause resistances to go below zero, so we're mostly covered even in the worst case. Effects like Heavy Frost, Coming Calamity or Beacon of Azis to ignore resistances are also handy.

Ok, but how do I fit 100 more spirit?

Well, the most straightforward way is a Sceptre offhand. On Amazon, Lycosidae is the hyped offhand (or Sacred Flame if you're rich), but Accuracy has massive diminishing returns. So doubling it doesn't anywhere near double the benefits you get from accuracy. For me, it's around a 20% DPS increase, which is nothing compared to what Trinity does. In the right setup, Trinity can even outperform Sacred Flame. And because Sacred Flame is "as extra", it will always mess with Trinity making them mostly incompatible, at least with the tools we have right now.

https://poe2db.tw/us/Sceptres

A Sceptre rolls 100 spirit at base, but can roll explicit mods to increase that to over 200. They also come with free auras, like Malice, Purities or Discipline. Personally, I run discipline for 200+ base ES to make up some of the defense loss of running with no shield. Malice is cool on paper, but unless you're a melee build, most things aren't going to be in your "presence" long enough for it to do anything. They can also roll mana and Strength or Intelligence to help with your stats, save some suffixes elsewhere.

What does this all look like?

Here's my very work in progress PoB on LS Amazon: https://poe2.ninja/pob/2720

The sceptre offhand gives me enough spirit for Trinity, Ghost Dance, Wind Dancer, Combat Frenzy, Herald of Thunder and I still have spirit left over for another Herald or some persistent support gems. My gear is pretty mid, lots of 5-10ex pieces and a couple good ones. CI "From Nothing" jewel gets you Heavy Frost, which makes sure bosses hit 0 resists even after map mods.

I was hoping Elemental Sundering would play into all this, as I'm able to apply all the ailments between Infusion and Storm Lance, but that skill is very weird. The animation causes a big delay between pressing it and actually doing damage, and at least in my testing something about the damage seems off. Testing on that skill is probably a whole other post though.

For clearing, I get Innervate and Ice Bite so I cap on 2 resonance, and those extra buffs help to one shot rares. I tried setups to have all 3 but it was inconsistent at best. Storm Lance single target doesn't have any type of "gained as" so it caps all 3 resonance, because it hits quickly and does even damage across all 3 elements.

TLDR

Use a cheap Sceptre to fit Trinity. Wear an even roll Painter's gloves. Get an easy and massive damage boost to your elemental build.

Quick note I'm not sure where to put: Important gem level breakpoints are 20, 22, and 25 for 12%, 13% and 14% respectively. It can hit level 32 for 16% with a very specific setup, but I don't think it's worth going farther than level 25.